1. Field of the Invention
Generally, the present invention relates to the speaker systems and methods. More specifically, the present invention relates to a speaker systems and methods having amplitude and frequency compensation as a function of ambient noise.
2. Description of the Related Art
In the field of speaker system design and implementation, many factors play a decisive role in determine, for example, what types of speakers to use, how large the speakers should be, what frequency response the speakers should have, and so on. One of the more important off these factors is the environment in which the speakers must operate. Specifically, the frequencies and amplitudes of the ambient noise surrounding the speakers-operational area must be considered.
Conventional speakers of today are utilized, for example, to present audio or audio/video advertisements in commercial and retail store environments where ambient noise levels may vary widely over time. It is known in the audio field that the intelligibility of reproduced speech or music sound in such environments, derived from an audio program signal, is strongly affected by the ratio of the volume of the reproduced sound to the volume of ambient noise. Intelligibility may therefore be enhanced by processing the audio program signal in such a manner as to vary the volume of the reproduced sound directly as a function of the volume of the ambient noise. Further, it is known in the audiology field that the intelligibility of a hearing aid microphone output signal containing both live speech and ambient noise signal components can be enhanced through a signal process that introduces both compressed gain and increasing high frequency feedback in response to decreasing amplitude of such speech and noise signal.
For example, U.S. Pat. No. 3,934,084 to Munson describes an audio amplifier system that includes a variable gain amplifier adapted to receive an input signal, means for detecting periods when the input signal falls below a predetermined level, and sound transducer means arranged to provide a signal proportional to the sound level in the area or part thereof covered by the system for controlling the gain of the amplifier. An inhibitor is provided which is arranged to be controlled by the detecting means so as to prevent any change of the gain of the variable gain amplifier except during periods when the input signal falls below the said predetermined level.
FIG. 1 illustrates a typical audio/video speaker system as is know in the art today. As shown in FIG. 1, the audio program input signal Sin, typically consisting of summed left and right stereo signals, is applied to signal input s of prior art signal process P1. P1 output port o provides signal process output signal Sout1. P1 introduces transfer function f1 providing continually increasing gain of Sin with increasing amplitude of a signal process control signal described below. Microphone MIC1 provides an output signal S1 applied to level detector D1, which provides an output DC microphone signal S2 applied to signal input s of electronic switch E1. Sin is also applied to level detector D2, which provides an output DC program signal S4 applied to control input c of electronic switch E1. S2 transfers to signal output o of electronic switch E1, providing signal process control signal S3 only when DC program signal S4 is in the off state, which occurs when Sin is below a minimum threshold level. S3 is applied to control input c of signal process P1 and thereby determines transfer function f1.
Such conventional speaker systems provide amplitude compensation linearly and directly as a function of the changing ambient noise. This linear compensation is a transfer function f1 expressed by the equation f1(San)=(Sin×San), where Sin is the program input signal amplitude and San is the ambient noise signal amplitude. However, the above linear transfer function is non-optimal for at least retail store and other commercial environments, which commonly exhibit frequent and widely varying changes in ambient noise, since the conventionally compensated speaker output signal provides commensurately frequent and widely varying changes in sound levels that can be annoying to listeners. Thus, what is needed is a speaker system providing direct, but incremental, amplitude compensation as a function fi of such frequent and widely varying changes in ambient noise.